There are some authors for whom writing is simply one of the many strings to their bow, and Eleanor Updale is a prime example of this breed. When not writing, she, among other things, works at the University of London, sits on the clinical ethics committee at Great Ormond Street Hospital, is a trustee of the Gulbenkian Museum Prize, and panel-beats the dents out of Chinook helicopters at her local RAF base. I made that last one up, but you get the idea.

How she finds the time to write, I don't know, but the results are mightily impressive, that's for sure. Some people just write very well. I don't mean that they're necessarily good at plot or characterisation or whatever, I simply mean that they have a way of putting words on the page that immediately communicates with the reader, and Updale certainly has that talent in spades. The fact that she also does great characters and plotting makes reviewing this book a pleasure.

Montmorency and the Assassins is the third book in which her protagonist, Montmorency, appears. In a former life he was Scarper the thief but, having been badly injured in an accident and nurtured back to health by Dr Farcett, he has reinvented himself as a wealthy gentleman (with the affectations of no first name and always travelling with large amounts of luggage), though his seedy alter ego "had crept up on him time and time again". In previous encounters, Montmorency has done undercover work for the British government. Here he starts off working a private case.

This particular adventure is set at the very end of the 19th century, as Queen Victoria's reign is drawing to a close. Updale is not afraid to mix real people with her fictitious characters and to give us an insight into Victorian ideas, events and inventions, though her writing rarely preaches and, even more importantly, never veers into pastiche. Here we spend time with prospective assassin Gaetano Bresci, meet Puccini and Thomas Edison, and encounter some ingeniously employed X-rays.

Montmorency and the Assassins is a thumping good story told with consummate skill. There's pace, action, excitement and humour, with characters you really care about. This time around, what starts out as a hunt for some rare specimens stolen from an eminent naturalist soon turns into a tale of international socialist revolt when Frank (Francis), the nephew of Montmorency's friend and companion Lord George Fox-Selwyn, gets mixed up with a bunch of student anarchists. This at a time when Europe is undergoing not only upheaval and assassinations but also a flu epidemic, which reaches US shores just as Montmorency does.

The story portrays both sides' points of view and is laced with a melancholy rarely present in children's literature today. There's great sadness on many levels and a shocking ending even for those familiar with what history had in store. Death stalks historical and fictitious characters alike, in the form of illness, murder and bloody suicide. Updale doesn't pull any of her punches.

There's no need to have read the previous two books to appreciate this adventure, so, in that sense, it's a stand-alone title. But it'll be an even richer, more moving experience should you read all three chronologically. I've no doubt that Updale is already working on a fourth ... along with 101 other things, of course.

· Horrendous Habits, the second of Philip Ardagh's Further Adventures of Eddie Dickens, is published by Faber in July.